Night Traffic Flow Simulator (2D)

Traffic Density

Cars on the road 28

Speed Limit

Desired speed 65 km/h

Traffic Signal

Cycle length 18 s

Green share 55%

Night ring road — headlights on, watch the jam waves form.

Live Readout

Avg. speed

0 km/h

Throughput

0 /min

Congestion

Cars

How it works

Every car on this ring road drives the Intelligent Driver Model (IDM), the same car-following physics used in real traffic-engineering software. Each driver picks an acceleration from four ingredients: how far it is from its desired speed, how close it is to the car ahead, how fast that gap is closing, and a minimum safety buffer plus a reaction-time headway. There is no scripted braking — jams, stop-and-go waves and free flow all emerge from those local rules alone.

A stop line partway around the loop cycles between green and red on the timer you set. A red light is treated by every approaching car exactly like a stationary vehicle parked at the line — the same IDM math that keeps a safe gap behind a real car also brings drivers smoothly to a halt at red and releases them on green, which is why a bad cycle length can trigger a jam even at low density.

Throughput counts cars crossing a fixed reference point on the road per minute — the real-world measure of how much traffic a road can actually carry. Raising density past a critical point drops both average speed and throughput at once: the classic traffic-flow "capacity drop" that makes highways less efficient once they're too full, even though every driver is still trying to go as fast as possible.

Headlights (front) Taillights (rear) Signal green / red